success and fitness. For example, according to optimal foraging theory
animals will forage preferentially in areas where prey density is highest
( Krebs &
Davies, 1978). (Prey can refer to plants as well as animals)
Although density estimates are usually thought to occur with time estimates
(a combination of inter-prey intervals), they might also occur with count
estimates (the number of prey) or rate estimates (the number of prey in a
fixed time interval). An excellent set of chapters and references on
optimal foraging theory is found in Kamil and
Sargent ( 1981).Of course, it is possible that animals in a laboratory situation will
provide evidence of capacities which have not been used as yet In nature.
Such "prospective" evolution may result from (1) the natural selection of a
general-purpose device that is likely to be successful in varied and
changing environmental circumstances, (2) a concomitant development
dependent upon the natural selection of some other specific capacity, or
(3) the random variation in the evolution of cognitive abilities through
speciation (e.g., Gould, 1980; Gould &
Eldredge, 1977). This is in contrast
to the natural selection of special-purpose devices that are proven
successful in particular environments. For timing, counting, and rate
discrimination, a single general-purpose accumulator may have evolved that
can be operated in several modes (e.g., Run, Stop, and Event) rather than
separate devices sensitive to temporal, numerical, and density attributes of
a stimulus.

ACKNOWLEDGMENTS

This research was supported by NSF Research grants BNS 79-04792 and BNS
82-09834.

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